Control system for hydraulic circuits



Dec. 8, 1964 B. J. \VOOLLEY ETAL CONTROL. SYSTEM FOR HYDRAULIC CIRCUITS Filed June 12, 1961 4 Sheets-Sheet l dem e5 7; Woo //ey 5mn/f IVM/AW, INVENTORS.

A HNE KJ' 4 Sheets-Sheet 2 daf/77e 5 7. Wop //ey .5mn/n f lI/Qo Meg, INVENTORJ,

' BY f4/ 4770 /VEVJ Dec. 8, 1964 B. J. wooLLEY ETAL.

coNTRoL SYSTEM FoR HYDRAULIC CIRCUITS Filed June 12. 1961 Dec. 8, 1964 B. J. wooLLEY E'rAL 3,159,965

CONTROL SYSTEM FOR HYDRAULIC CIRCUITS Filed June 12, 1961 4 sheets-sheet s Ja M /l ,ff 47 Y TW y J JJ @y J Dec. 8, 1964 B. J. wooLLEY ETAL 3,159,965

CONTROL SYSTEM FCR HYDRAULIC CIRCUITS 4 Sheets-Sheet 4 Filed June 12, 1961 INVENTORS,

Arr /VEVJ United States Patent O ice 3,159,965 g CONTROL SYSTEM FOR HYDRAUMC CRCUITS Brown 5. Woolley and .l ames D. Woolley, both of R0. Box 1249, Kilgore, Tex. Filed .lune 12, 1961, Ser. N 116,593 11 Claims. (Cl. 60-19) This invention relates to a control system for controlling a prime mover such as an engine, and more particularly Iit relates to such a system which is responsive to the load applied to said prime mover.

In many industrial applications, hydraulic circuits including a supply pump driven by a prime mover, such as an engine, are employed to properly actuate a device, apparatus or tool. It is desirable to permit the hydraulic circuit to be maintained in idling or no-load condition when the device actuated by said circuit is not in use, and yet said circuit must be capable of automatically adjusting itself to full load or maximum output upon the application of a useful work load to the circuit. Such a circuit is particularly desirable where the hydraulic output or load imposing device is located some distance remote from the hydraulic pressure supply Ypump and the prime mover which drives the pump. An example of such an application may be found in the drilling industry wherein hydraulically operated pipe tongs are located on the drilling rig oor where they are to be used while the prime mover, such as a gasoline engine, and the pressure supply pump are located in the power generation area. As is well known, applying a load to a hydraulic circuit when said circuit is under idling conditions will result in overloading with the consequent inoperativeness of the circuit due to stalling of the prime mover unless some means is provided whereby the output of the prime mover and pressure supply pump for the circuit may be increased either before the load is applied to the circuit or contemporaneously therewith.

In the past, the art has attempted by various means to provide for automatically increasing the output of the prime mover when a load is applied to the hydraulic circuit of which the pump is a part. Probably the most common of the prior art systems is that in which the increase in the pressure supply or pump output line occurring when the load is applied to the circuit is sensed or taken at one point in the pump output line and utilized to acutate a controller which, in turn, causes Van increase in the output of the pressure supply pump, as by opening the throttle of a gasoline engine which drives the pump. Such a control system has a serious disadvantage in that the engine frequently stalls and becomes inoperative due to the greatly increased load applied thereto before the speed and consequent output of said engine can be sufficiently increased. It is believed that this fatal delay is primarily due to the lack of sensitivity in sensing the increase in pressure at a single point in the pressure supply line early enough to provide the necessary time for opening the throttle and increasing the operating speed of the engine. Also, the single point sensing system is unable to differentiate between the change in pressure due to the application of a load to the circuit and a change in pressure due to some other circumstance, such as a change in uid velocity or viscosity.

It is therefore a primary object of this invention to provide a control system for a hydraulic circuit which allows'the circuit to operate in a no-load or idling condition and yet is capable of automatically adjusting and adapting said circuit for operation under a loaded condition without failure of the circuit as would be occasioned by stalling of the prime mover upon application of the load.

An important object of this invention is to provide a control system of the character described wherein the increase in pressure in the pump output line resulting from the application of the load to the hydraulic circuit is sensed or taken at two spaced apart points in said output line, and such sensing is utilized as the controlling factor, whereby a high degree of sensitivity to changes in pressure in the circuit is obtainable to actuate a proper controller.

A further object of this invention is to provide a novel control system having means which is responsive to a comparatively slight change in the pressure in the pump output line for increasing the output of the hydraulic pressure supply pump.

A still further object is to provide a system wherein the control means includes a readily adjustable, movable actut ator member which is fulcrum mounted and which is responsive 'to pressures from two spaced apart points on the pump output line so that the moments due to the two pressures acting in opposition to one another about the fulcrum of said actuator member are varied in accordance with changes in said pressures to effect movement of said actuator member.

.Another object is to provide a control system for a hydraulic circuit which is particularly adapted for use with a hydraulically operated tool or device, such as pipe tongs, and which operates in such a manner that when hydraulic power is required for operation of the tool or device, such power is readily available.

The constructionV designed to carry out the invention will be hereinafter described, together with other features thereof.

This invention will be readily understood from a reading of the following detailed description and reference to the drawings wherein like numerals refer to like parts and wherein:

FIGURE l is a schematic illustration of a control system constructed in accordance with the invention and illustrating the same applied to the hydraulic actuating circuit of a power-operated tool or apparatus;

FGURE 2 is a schematic illustration showing the invention applied to a modified hydraulic circuit;

FIGURE 3 is a schematic illustration of another moditication of a hydraulic circuit to which the control system of this invention is applied;

FIGURE 4 is a sectional view of the actuator device forming part of the control system;

FIGURE 5 is an isometric view of the inner block forming part of the actuator device;

FIGURE 6 is a sectional view taken along line 6-6 of FIGURE 4; and

FIGURE 7 is a sectional view taken along 7-7 of FIG- URE 4.

In the drawings (FIGURE 1) the usual simple type of hydraulic circuit, which is employed for controlling the operation of a power operated tool, is illustrated, and such circuit includes a prime mover 1li which drives a hydraulic pressure supply pump 11 by means of the connecting shaft 12. The prime mover may conveniently be either an internal combustion engine or an electric motor but as described herein will be referred to as an internal combustion engine having the throttle control ltla. The output side of the pump 11 has connection through a conductor 14 with the hydraulic motorv 15, and when said motor is operated it actuates a power operated tool 17, which tool is schematically illustrated as the usual pipe tongs used in well drilling. A line 1S extends from the hydraulic motor back to the inlet side of the hydraulic pump 11, and when the tool 17 is being actuated the circulation of hydraulic fluid is from the pump, through conductor 14, through motor 15 and then back to the pump through the return line 18. A three-way valve 19 is mounted in the conductor 14 at the inlet side of the hydraulic motor and has connec- Patented Dec. 8, 1964` 3. tion with a by-pass line 20 which `provides for a bypass of hydraulic iluid around the motor 15. c

When the tool 17 is inactive and there is no requirement for operation of the hydraulic motor 15, the threeway valve .19 is positioned so as to by-pass lluid around said motor, and said hydraulic iluid merely circulates through the hydraulic circuit. At this time, the throttle control 10a of the engine is adjusted to an idling speed so. that the pump 11 is operatedV at what might be termed an idling or no-load condition since the hydraulic circuit is underrno substantial load. When it is desired to actuate the tool or pipe tongs 17, the three-way valve 19 is actuated to directhydraulic fluid to the motor l5. This immediately places a load upon the hydraulic circuit, and it is necessary that the throttle control 10a be actuated to increase the engine speed sutliciently to operate the pump to take care of the load condition. It mightV be noted that in actual practice the throttle control 10a is moved from yidling or no-load condition to wide open or full-load condition. If this adjustment is not made at the time that the tool is to be operated, stalling of the engine 10 will occur and the entire hydraulic system will become inoperative. Y

The foregoing describes one type of hydraulic circuit which is normally employed in operating a power operated tool. vOt course, it is evident that the engine 10 may be an electric motor, in which event the control 19a would properly control the speed of such electric motor. The

particular details of the hydraulic circuit form no part of the present invention, and therefore the particular circuit is subject to variation.

For controlling the adjustment of the throttle control 10a to increase the engine speed under load conditions, which is at the time that .the three-way valve is actuated to direct hydraulic lluid to the motor 15, a control system which is included within the dotted lines A in FIGURE l is provided. This control system comprises an actuator device 21, vwhich will be hereinafter described in detail and which controls through a suitable line or connection 22 the position of the throttle control 19a. The actuator device, as will be explained, is operated by the conditions in the pump outlet conductor 14 and is connected to said conductor through two spaced apart lines 14a and 14b which connect with theA conductor 14 atthe points designated B and C.

The pressure at point B in the pump outlet conductor 14 is upstream of the point C and is therefore always greater than the pressure at point C by the amount of pressure drop naturally occurring between points B and C in the conductor 14. Preferably the points B and C are sufficiently spaced apart so that the pressure drop or differential therebetween is at least of the total circulating pressure of the hydraulic circuit. It is evident that .the pressures at points Band C vary directly with the pressure inthe pump outlet conductor 14 as well as proportionately with one another according to the aforesaid pressure drop between the two points. By soV arranging the sensing points, two pressures which are always unequal are supplied to the actuator device 21 through the communicating lines 14a and 1415.

When the hydraulic circuit is operating under rio-load or idling conditions, the actuator device 21 is set so that the throttle control a is adjusted to permit the engine or prime mover 19 to runat idling speed. When the valve 19 is opened to direct hydraulicuid to the motor land thereby impose a load ,upon the circuit, there is an immediate back pressure or surge created in the pump outlet Vconductor 14 which results ina substantially `instantaneous increase in pressure at ypoints B and C. As will be explained, this sudden increase in pressure at points B and C operates the actuator 21 which, in turn, moves the throttle control 10a to increase .the output of the prime mover or engine 10. Because the actuator y21vis operated substantially instantaneously with the application of the increased load to the hydraulic circuit, the output of the engine ltlis increased to increase the outi shown in FIGURES 4, 5,6 and 7 and includes an outer housing D having a chamber 23 therein and closed on one side by a cover plate 24 (FIGURE 6). Mounted for limited movement in one direction withinV the chamber 23 is an inner block E which is shown isometrically in FiG URE 5. An elongate slot 25 is provided in one end of the inner block E and extends longitudinally thereof. Flange portions 26 project outwardly from the side walls 27 and 2S which are on opposite sides of the slot 25, and these `flange portions 26 are centrally located with respect to such side walls. The side wall 27 is uninterrupted while a portion of the opposite side wall 2S is cut away so that the recess 29 is formed therein, such recess 29 communicating with the elongatefslot 25. 1

When the inner block E is properly positioned within the chamber 23 of the outer housing D, such inner block E is confined against movement in one direction by the side wall of the outer housingD and the cover 24, while movement from left to right, as viewed in FIGURE 4, is prevented .by the iiat spring 39 engaging the flange portions 26 on the inner block E, thereby forcing the kedge 3l of the inner block E against the` opposite-wall of the chamber 23. In order that the inner block E may be adjusted or moved upwardly or downwardly, as viewed in FIGURE 4, it is resiliently confined between a spring 32, which engages a recess 33 within one side of said block, and an adjusting screw 34 threaded through the outer housing D and engaging the opposite side of the block. The spring 32 also engages a screw 35 which is threaded through the wall of the outer housing D so that the spring 32 may be conveniently removed or replaced. It is believed obvious that the inner block E may bemoved or adjusted upwardly or downwardly as viewed in FIGURE 4 by simply rotating the adjusting screw 34.

An actuator member 36 is disposed within the elongate slot 25 of the inner block E between the ange portions 26, and such actuator'member 36 is pivotally mounted upon a fulcrum shaft 37, which shaft is supported by said iiange portions 26. A suitable bearing, such as ball bearing 3S, is interposed between the shaft 37 and the actuator member 36 to minimize the frictional resistance to movement of the member.

The actuator member or Ybar 36 engages a control switch 39 mounted within the recessed portion 29 in the innerblock E, whereby when the actuator bar moves it actuates or energizes the switch 39 and the connection 22 which, as noted above, extends to the throttle control 10a. In order thattthe location of the switch 39 may be adjusted laterally with relation to the actuator bar 36, said switch is `mounted on an adjustable plate 40 within the recess 29. Slots 41 formed in the plate 40 receive screws 42 which are threaded into the bottom of the inner block E and which have their heads overlying the plate; thus, the base plate 40 and attached switch 39 may be frio tionally held in various adjusted positions.

For controlling the movement of the actuator bar 36, a pair of cylinders 43 and 44 are provided. Such cylinders are preferably circular 4in cross-section and are adapted to fit in the bores 45 and 46 in the outer housing D. The cylinders are held in place by split or snap rings 47, and the O-rings 43 provide a seal between the outer housing D and the outer. periphery of the cylinders 43 and 44. The hydraulic pressure lines 14a and 14h which convey the pressure sensed at points B and C, respectively, to the actuator device 2l are suitably connected to cylinders 43 and 44, respectively', as by threads 49.

A piston means is provided in each of the cylinders 43 and 44 and, in the preferred form, the piston means comprises a plurality of balls Si) in lieu of the ordinary cylindrical piston. These balls are preferable because they present less frictional resistance to movement than does the usual cylindrical piston, they eliminate the necessity for connecting rods, and they allow for a more cornpact and practical design. Also, it has been found that providing a clearance of .0001 to .0004 inch between the balls 50 and the wall of the bore 51 in each cylinder is very advantageous in that contaminants such as grit or other solid particles are allowed to by-pass the balls. Without such a by-pass feature, the contaminants would reduce the sensitivity of the device by restricting the ease of movement of the balls and would eventually cause the freezing or locking thereof. The inner ends of the cylinders 43 and 44 are sufliciently spaced from the actuator member 36 so that the innermost ball 59a in each of the cylinders may be -in contact with said member and yet be supported by or contained at least partially within said cylinders. The adjusting screw 34 acting against the spring 32 provides the means whereby'the actuator member 36 is adjustable, so that the point of contact between the innermost balls 50a in each cylinder and said member may be varied with respect to the fulcrum shaft 37.

The flat spring 30 functions to hold the fulcrum point or shaft 37 of the actuator member 36 a predetermined distance from the ends of the cylinders 43 and 44 along a line parallel to the axis of such cylinders (left to right as viewed in FIGURE 4), even though the device may or may not be subjected to hydraulic pressure. A flat or leaf-type spring is preferred because -it will allow movement or shifting of the inner block E and actuator member 36 along a line perpendicular to the axis of the cylinders 43 and 44 (upwardly or downwardly in FIGURE 4) while always performing the aforementioned function. It is obvious that the spring 30 could be located at other positions, as between the edge 31 of the inner block E and the wall of the chamber 23 opposite the cylinders 43 and 44, and still maintain the parts in the desired relationship.

As noted above, the switch 39 provides the means for activating or energizing the connection 22 whereby the throttle control a may adjust the operation of the prime mover 10. If the throttle control 10a is a well known solenoid, then the switch 39 is preferably a highly sensitive microswitch which will activate the throttle control llla electrically through the connection 22. The usual switch plunger 52 of such a microswitch coacts with the actuator member 36 so that as it pivots or tilts about the fulcrurn shaft 37 the resulting motion of the plunger 52 will open or close the electrical circuit through the connection 22.

lf a common two-position three-pole microswitch is used as the switch 39, then the connection 22 would comprise electrical leads attached to the switch 39 at the common terminal 39b and one of the terminals 39a or 39e depending upon whether the throttle control 10a is to be energized when the plunger 52 is extended or retracted. As it has been assumed that the pressure lines 14a and 141: are connected to cylinders 43 and 44 respectively, it will be also assumed, for the purposes of this discussion, that the switch 39 will actuate the throttle control 10a when the switch plunger 52 is in the retracted position which closes the circuit between the common terminal 39b and the terminal 39a. It is apparent that the various parts and connections could be reversed so that as the actuator bar 3% pivots or tilts about the yfulcrurn 37, it will allow the plunger 52 to move to its extended position thereby actuating the throttle control 10a. The passageway 53 in the inner block E and the passageway 53a in the outer housing D provide the openings through which the connection 22 may extend outwardly to the exterior of the housing.

As discussed previously, there is a slight clearance between the balls 50 and the bore 51 of the cylinders 43 and 44 so that a small `quantity of hydraulic tluid may enter the chamber 23 in the outer housing D and, in order that excessive amounts of this iiuid may be removed, a drain'opening is provided in the outer housing 23 which communicates with the chamber 23 and the recess 29 of the inner block E. A drain line 54 conveys the hydraulic tluid to a suitable reservoir. O-f course other drain passages such as that designated at 55 may be provided at convenient loc-ations in the outer housing D.

In operation of the actuator device 21 in a circuit such as that shown in FIGURE l, hydraulic liuid'under pressure is supplied to the cylinders 43 and 44 through the hydraulic 14a and 1412. As noted previously, lthe pressure supplied to the cylinder 43 through the line 14a is representative of the pressure in the pump output line 14 at point B, Iwhile the pressure in the cylinder 44 is representative of that pressure at point C in the pump output line 14. The pressures thus supplied to the cylinders 43 and 44 act upon the balls S0 and force the innermost ball 50a in each cylinder against or in contact with the actuator member 36. The actuator member 36 is initially adjusted by means of the adjusting screw 34 while the circuit is operating under idling or no-load conditions so that the actuator member 36 does not depress the switch plunger 52, and the actuator member 36 is .in a balanced position, that is, the edge 36a of the actuator member 36 which coacts with the switoh plunger 52 lies in a plane perpendicular to the axis of the cylinders 43 and 44. This balanced position is obtained by varying the distance between the fulcrum shaft 37 and the point of contact between the balls 59a and the Iactuator member 36 so that the edge 36a will lie in a plane perpendicular to the axis of the cylinders 43 and 44 when the moments about the fulcrurn shaft 37 due to the action of the balls 50a against the actuator member 36 are equal. As the pressure at point B in the pump output line 14 is greater than the pressure at the point C, the force acting upon the actuator member due to the pressure in the cylinder 43'is greater than the force due to the pressure in cylinder 44, and the moment arm or distance from the center of the -fulcrum shaft 37 to the point of contact between the ball 50a in cylinder 43, and the actuator member 36 be proportionately less than the distance between the center of the fulcrum shaft 37 and the point of contact between the ball 50a in cylinder 44 and the actuator member 36. For purposes of illustration, it may be amumed that the pressure at point B is 50 psi. and the pressure at point C is 25 p.s.i., while the circuit is operating under idling or no-load conditions. As these pressures ultimately force the balls Sila against the actuator member 36, such actuator member must be adjusted so that the moment arm for the .pressure C is twice the length of the moment arm for the pressure B, whereby the moments acting in opposition to one another about the fulor-um shaft 37 are equal and the actuator member 36 is balanced. For instance, -using the pressure quantities noted above, the moment arm `for the pressure B may be one inch and the moment arm for the pressure C would be two inches, so that the two moments of fifty inch-pounds each cancel or nullify one another.

Once the actuator member 36 is adjusted or set in the balanced position by means of the adjusting screw 34, as discussed above, changes in the pressures due to fluid velocity and temperature variations will not spoil or disrupt the balance because such pressure changes are proportional; that is, a ten percent rise in the pressure would result in a pressure of 5S p.s.i. at point B and 27.5 p.s.i. at point C, and it is obvious that the moments due to such pressures would be equal and the actuator member 36 would not tilt or pivot about its fulcrum 37.

When the three Way valve 19 is switched from the bypass or no-load position to the working or loaded position, hydraulic tluid is conveyed to the hydraulic motor 15, and there is a resultant change in the pressure in the pump output line 14 due to the additional load imposed on the hydraulic circuit by the hydraulic motor 15. Continuing the above illustration, the pressures may be increased by twentypsi., which is the additional pressure required to drive the hydraulic motor when no load is applied thereto. The pressure at point B then becomes 70 psi., and its moment becomes seventy inch-pounds, while the pressure at point C increases to 45 psi., and its moment increases to ninety inch-pounds. As these momentsk are no longer equal, theactuator member 36 is in an unbalanced state and it pivots about its fulcrum 37, thereby actuating the switch 39 which, as noted above, ultimately results in increasing the output of the pnime mover 10. Y

If the hydraulic motor 15 in the above illustration had a yload connectedthereto when the three-way valve 19 was changed to the Working position, then the additional pressure required to drive the motor with its load would have been considerably greater; for instance, 2,000 p.s.i. Pressure B would thus increase to 2,050 p si., and its moment would then `be 2050 inch-pounds, while C would increase to 2,025 p.s.i. and its moment would become 4,050 inchdpounds, thereby creating a similar unbalanced condition with respect to the actuator member 36.

By dividing the pressure at C by the pressure at B, the percentage .relationship .of the pressures is obtained, and the difference between such percentages is an expression of the unbalance created by the change in` pressures. Using the above gures .for illustrative purposes, the percentage relationship of C:B under no-load conditions is 25/50 or iifty percent. The relationship changes to 45 70 orapproximately 64.3 percent` when the three-way valve 19 is positioned so that the iiuid passes to the unloaded hydraulic motor 1S. The difference of 14.3 percent between the two percentages in the two sets of circumstances is said to be the percentage unbalance. Of course, so long as the pressure percentages remain the same, even though the pressures themselves vary, the actuator memberl remains balanced and stationary. By using the well known microswitch which requires only la slight force for actuation thereof, the actuator device 21 is sensitive 8 of the pump 11 through the hydraulic line 59. The well known relief valve 57 is placed in the pump output line 14, as is the control valve 58. A relief line 60 1s provided which communicates with the relief valve 57 and the tank 56 so that any excessive pressure may be relieved or vented to the tank 56. The control valve 58 maybe the well lmown three-way type and communicates with the tank 56 by means of hydraulic lines 61 and 60. Thiscontrol valve 5S provides 'a means whereby the actu-V ator device 21, the three-way valve 19 and the hydraulic motor 15 may be rendered inoperative. accomplished by positioning the control valve 58 so that the hydraulic uid from the pump 11 in the line 14 is bypassed to the tank 56 by means of lines 60 and 61.

The control system A, as discussed above, is incorpo rated `in the FIGURE 2 circuit and accomplishes the same function as in the FIGURE l circuit; that is, it provides a means for automatically increasing the output of the prime mover 10 when the load applied to the circuit is increased. Although the pressure sensing points B and C may obviously be located at other points in the pump output line 14, the point B in the hydraulic circuit shown in FIGURE 2 is preferably located in pump output line 14 between the output connection of pump 11 and the inlet connection of relief valve 57, and the point C is preferably Ilocated in the pump output line 14 downstream of the control valve 58.

The hydraulic circuit shown in FIGURE 3 is the dual I pump manifold type and is commonly known as a highenough to begactuated by a percentage unbalance of .2 t

of one percent. 1

It is believed obvious that devices other than the common microswitch could be substituted for the switch 39 which would adequately provide the means for activatingV or energizing the throttle control 10a. For instance, a three-position microswitch or two double position microswitches may 'be effectively utilized to activate the throttleV control 10a through the connection 22 .if the actuator member 36 pivots or tilts ineither direction. Other well known switches could be provided which `would allow for operation of the prime mover .at outputs between idling and maximum according to the extent or degree of the movement of the .actuator member 36. The output of the prime mover 10 could then be varied through an intinite number of positions in the range between idling and maximum output by substituting for the switch 39 a rheostat or potentiometer responsive not only to the movement of the actuator member 36 but also responsive to and varied by the extent of such movement. Also, any one of the well known types of servo mechanisms could be effectively utilized to duplicate or exaggerate the movement and/ or position of the actuator member 36.

The control system A including the actuator device 21 may obviously be keffectively utilized in more complex hydraulic circuits than that shown in FIGURE Yl. For instance, the hydraulic circuit shown kschematically in FIGURE 2, commonly known as the single pumpmanifold type, includes the basic circuit shown in FIGURE 1 together with a hydraulic uid reservoir or tank 56, a relief valve 57 and a control valve 5S. The hydraulic uid return line 18 communicates with the reservoir or tank 56 instead of the pump 11, as shown in FIGURE 1,

and the tank 56 communicates with the input connection y low system. It contains all of the elements of the circuits shown in FIGURES 1 and 2 together with an additional hydraulic pressure supply pump 11a, an unloading valve y62 and ka check valve 63. The prime mover 10 drives boththe high pressure pump 11 and the low pressure pump 11a by means of shafts 12 and 12a respectively. The low pressure pump 11a communicates with the un loading valve 62 by means ofthe pump output line 14, while the high pressure pump 11 is connected to the unloading valve 62 through hydraulic line 64. 'Ihe well known unloading valve 62 is actuated by the pressure inthe line 64 and is set to unload or relieve the low pressure pump at a predetermined pressure by means of line 65 which communicates with the tank 56 through connection with the bypass line 60. The check valve 63 is preferably placed between the unloading valve 62 and the relief valve 57 in the pump output line 14, and it functions to prevent reverse flow in the line 14; that is, it'prevents ow from right to left as viewed in FIGURE 3. The high pressure pump output line 66 communicates with the pumpl output line 14 and the relief valve 57, which valve prevents overpressuring of the circuit.

Thecontrol system A may be conveniently incorporated in the FIGURE 3 circuit by locating the pressure sensing point B in the pump output line 14 between the low pressure pump 11a and the unloading valve 62, while the pressure sensing point C is located in the line 14 downstream of the control valve 53 as in the FIGURE 2 circuit. The control system A will then perform the same function as in the previously described circuits, and the output of the prime mover 10 will be automatically increased upon an increase in the load applied to the system.

The foregoing disclosure and description of the invention s illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made within the scope of the appended claims without departing from the spirit of the invention.

This may be Y 9 points in said conduit, and meansoperatively associated with said sensing" means actuated only by a change in the pressure differential between said spaced points resulting from the back pressure created when a load is applied to the hydraulic circuit by the load-imposing means, said last-mentioned means when actuated operating said actuator whereby the output of said pressure supply means of the hydraulic circuit is varied in accordance with the load imposed on the circuit by the load-imposing means.

2. The combination with a hydraulic circuit which includes a pressure supply means and a pressure supply conductor communicating the pressure supply means with a load-imposing device whereby pressure variations in said pressure supply conductor `are representative of the load imposed on the circuit by the load-imposing means, of a control system comprising "a control means, an operative connection between said control means and the pres` sure supply means whereby said control means controls the operation of said pressure supply means, means for sensing the pressure at two spaced apart points in said conductor, and means operatively associated with said sensing means actuated only by a change in the pressure differential between said spaced points resulting from the back pressure created when a load is applied to the hydraulic circuit by the load-imposing means, said lastmentioned means when actuated operating said control means whereby the output of said pressure supply means for the hydraulic circuit is Varied in accordance with the load imposed on the circuit by the load-imposing means.

3. A control system for controlling the output of a hydraulic pump for a hydraulic circuit in accordance with the load imposed on said circuit including, an actuator for controlling the operation `of said pump, a conduit communicating between said pump and a load-imposing means, means for sensing the pressure at a rst point in said conduit, means for sensing the pressure in said conduit at a second point spaced downstream from said rst point, and means operatively associated with both of said sensing means actuated only by a change in the pressure differential between said spaced points resulting from the back pressure created when a load is applied to the hydraulic circuit by the load-imposing means, said lastmentioned means when actuated operating said actuator whereby the output of said pump for the hydraulic circuit is varied in accordance with the load imposed on the circuit by the load-imposing means.

4. A control system for controlling the output of a pressure supply means for a hydraulic circuit, which circuit includes a hydraulically driven motor operatively associated with a load-imposing device, including, an actuator for controlling the operation of said pressure supply means, a conduit communicating between said hydraulic pressure supply means and said motor, means for sensing the pressure at two spaced points in said conduit, and means operatively associated with said sensing means actuated only by a change in the pressure differential between said spaced points resulting from the back pressure created when a load is applied to the hydraulic circuit by the load-imposing device, said last-mentioned means when actuated operating said actuator whereby the output of said pressure supply means of the hydraulic circuit is varied in accordance with the load imposed on the circuit by the lload-imposing device through the hydraulic motor.

5. A control system for controlling the output of a hydraulic pump for a hydraulic circuit which circuit includes a hydraulically driven motor operatively associated with a load-imposing device including, an actuator for controlling the operation of said pump, a conduit communicating between said pump and said hydraulic motor, means for sensing the pressure at a iirst point in said conduit, means for sensing the pressure in said conduit at a second point spaced downstream from said irst point, and means operatively associated with both of said sensing means actuated only by a change in the pressure differential between said spaced points resulting from the back pressure created when a load is applied to the hydraulic circuit by the load-imposing device, said last-mentioned means when actuated operating said actuator whereby the output of said pump of the hydraulic circuit is varied in accordance with the load imposed on the circuit by the load-imposing device through the hydraulic motor.

6. A control system for controlling the output of a pressure supply means for a hydraulic circuit, which circuit includes a hydraulically driven motor operatively associated with a load-imposing device including, an actuator for controlling the operation of said hydraulic pressure supply means, a conduit communicating between said hydraulic pressure supply means and said hydraulic motor, means for sensing the pressure at two spaced apart points in said conduit, and means operatively associated with said sensing means actuated only by a change in the pressure diierential between said spaced points resulting from the back pressure created whena load is applied to the hydraulic circuit by the load-imposing device, said last-mentioned means when actuated operating said actuator whereby the output of said pressure supply means of the hydraulic circuit is Vmaintained at a minimum output commensurate with that output required to operate said hydraulic motor when no load is applied thereto and whereby the output of said pressure supplyl means is increased to maximum output commensurate with that outl put required to operate said hydraulic motor when a load is applied thereto by said load-imposing device.

7. A control system for a hydraulic circuit having a hydraulic pressure supply means therein including, an actuator member pivoted about a fulcrum, means for applying pressure from one point in said hydraulic circuit to that portion of the actuator member on one side of the fulcrum, means forapplying a second pressure from a second point in said circuit spaced from said first point to that portion of the actuator member on the other side of said fulcrum, means for adjusting said actuator member to a balanced position when said pressures are applied thereto, means for varying the pressure in said hydraulic circuit according to the load imposed on said circuit, and means responsive to the movement of said actuator member when there is a change in said pressures due to the load imposed on said circuit causing an unbalance about said fulcrum for varying the output of said hydraulic pressure supply means.

8. The control system as set forth in claim 7 wherein the means for applying pressure to that portion of the actuator member on each side of the tulcrum comprises a cylinder and a piston, each piston being constructed of a plurality of balls of slightly less diameter than that of the bore within said cylinder adapted to transmit the pressure to that portion of the actuator member on each side of the fulcrum.

9. A control system for a hydraulic circuit having a hydraulic pressure supply means therein including, an outer housing, an actuator pivotally mounted about a fulcrum within said outer housing, a rst cylinder and piston means mounted in said outer housing and coacting with said actuator member for applying pressure from one point in said hydraulic circuit to that portion of the actuator member on one side of the fulcrum, a second cylinder and piston means mounted in said outer housing and coacting with said actuator member for applying a second pressure from a second point in said circuit spaced from said rst point to that portion of said actuator member on the outer side of said fulcrum, means for adjusting said actuator member to a balanced position when said pressures are applied thereto, means for varying the pressure in said hydraulic circuit according to the load imposed on said circuit, and means responsive to the movement of said actuator member when there is a change in said pressures dueto the load imposed on said circuit causing an unbalance about said fulcrum for varying the output of said pressure supply means.

l `l` 10. A control system for a hydraulic circuit having a hydraulic pressure supply means Vtherein inclu'ding,-an outer housing having a chamber therein, an inner Vblock mounted for limited movement Within said chamber, an actuator member pivotally mounted about a fulcrumcarried byssaid inner block, a first cylinder and piston for` pressure in said hydraulic circuit according to the load imn posed on said circuit and means responsive to lthe movement of said actuator member when there is a change in said pressures due to the load imposed on said circuit causing anunbalance about said fulcrum for varying the output of said hydraulic pressure supply means.

11. Acontrol system for controlling the output Vof a hydraulic pump for a hydraulicvcircuit in accordance with the load imposed on said circuit including, an engine driving said hydraulic pump, a throttle control for controlling the operation of said engine, a hydraulic motor operatively associated with a load-imposing device, an actuator for actuating the said throttle control, a conduit communicating between said hydraulic pump and said hydraulic motor, means for sensing,r the pressure at a first point in said conduit, means for sensing the pressure in said conduit at a second point spaced downstream Vfrom said first point, and means operatively associated with both of said sensing means actuated only by a change in the pressure differential between said spaced points resulting from the back pressure created when a load is applied to the hydraulic circuit by the load-imposing device, said lastmentioned means when actuated operating said actuator to actuate said throttle control whereby the operation of said engine is varied so that the output of said pump is varied in accordance with the load imposed on the circuit by the hydraulically driven motor operatively asso- Vciated with the load-imposing device.

References Cited in the le of this patent UNITED STATES PATENTS 2,309,415 Pearson et al. Jan. 26, 1943 2,440,981 Smith May 4, 1948 2,533,627 Roach Dec. l2, 1950 2,889,780 Binford u June 9, 1959 2,942,421 Hann et al -lune 28, 1960 

1. A CONTROL SYSTEM FOR CONTROLLING THE OUTPUT OF A PRESSURE SUPPLY MEANS FOR A HYDRAULIC CIRCUIT IN ACCORDANCE WITH THE LOAD IMPOSED ON SAID CIRCUIT INCLUDING, AN ACTUATOR FOR CONTROLLING THE OPERATION OF SAID PRESSURE SUPPLY MEANS, A CONDUIT COMMUNICATING BETWEEN SAID HYDRAULIC PRESSURE SUPPLY MEANS AND A LOAD-IMPOSING MEANS, MEANS FOR SENSING THE PRESSURE AT TWO SPACED APART POINTS IN SAID CONDUIT, AND MEANS OPERATIVELY ASSOCIATED WITH SAID SENSING MEANS ACTUATED ONLY BY A CHANGE IN THE PRESSURE DIFFERENTIAL BETWEEN SAID SPACED POINTS RESULTING FROM THE BACK PRESSURE CREATED WHEN A LOAD IS APPLIED TO THE HYDRAULIC CIRCUIT BY THE LOAD-IMPOSING MEANS, SAID LAST-MENTIONED MEANS WHEN ACTUATED OPERATING SAID ACTUATOR WHEREBY THE OUTPUT OF SAID PRESSURE SUPPLY MEANS OF THE HYDRAULIC CIRCUIT IS VARIED IN ACCORDANCE WITH THE LOAD IMPOSED ON THE CIRCUIT BY THE LOAD-IMPOSING MEANS. 